High voltage circuit for automobile engine ignition



Dec. 13, 1966 w. Y. PETERS 3,291,110

HIGH VOLTAGE CIRCUIT FOR AUTOMOBILE ENGINE IGNITION Filed Sept. 2, 19652 Sheets-Sheet 1 I N VE N TOR. W/ZZMM K 2-7521 Dec. 13, 1966 w. Y.PETERS 3,291,110

HIGH VOLTAGE CIRCUIT FOR AUTOMOBILE ENGINE IGNITION Filed Sept. 2, 19652 Sheets-Sheet 2 United States Patent 3,291,110 HIGH VOLTAGE CIRCUIT FURAUTGMGBILE ENGINE IGNITION William Y. Peters, Tucson, Ariz., assignor toJasper N. Cunningham, San Pedro, Calif. Filed Sept. 2, 1965, Ser. No.484,676 8 Claims. (Cl. 123-148) This invention relates to high voltagepulse generating circuits and, more particularly, is concerned with acircuit for use in the ignition system of automobile engines and thelike. This application is a continuation-in-part of application SerialNo. 382,149, filed July 13, 1964 and now abandoned.

With the higher speed, higher compression engines being used inautomobiles, the problem of generating a sufficiently high voltage forignition has become more severe. To use the standard breaker point andignition coil system, it became necessary to convert from a six volt toa twelve volt electrical system. However, even with the higher voltageavailable, there is still a problem of providing a reliable operationusing the conventional ignition coil for generating a high voltagenecessary for ignition. The primary of the coil requires substantiallylarge currents which results in pitting and corrosion of the breakerpoints. As a result, frequent adjustment or replacement of the points isrequired. Furthermore, any substantial reduction in the voltage on theprimary severely affects the energy of the spark. This means that coldweather starting or starting with a battery which is not fully chargedmay be difiicult because of failure of the ignition system to produce anadequate spark.

With the advent of the transistor, there have been a number oftransistor circuits proposed for ignition systems. Such circuits havenot proved entirely satisfactory because they have suffered from one ormore of the drawbacks that they have been too expensive, have notperformed well under extremely high temperature operating conditionssuch as encountered in the warm regions of the country, have beensensitive to drops in voltage of the battery source.

The present invention is directed to an improved high voltage ignitionsystem which provides high energy, high voltage output pulses which canoperate at high pulse repetition frequencies. The circuit utilizessilicon transistors to overcome temperature limitations, and operatesover a wide range of voltages. In addition, the circuit uses a minimumof components, is inexpensive to manufacture, is rugged and foolproof inoperation, and can be made much more compact than the standard ignitioncoil system.

These and other advantages of the present invention are achieved byutilizing a saturable core transformer having a high voltage secondary.The primary is connected in series with a capacitor and an inductoracross the battery source. A normally closed transistor switch connectsthe series junction point between the capacitor and the inductor to atap on the primary. The transistor switch is operated from the breakerpoints through a transistorized control circuit such that on opening ofthe breaker points, the transistorized switch is momentarily opened fora predetermined time interval causing a pulsing of the primary of thetransformer by energy stored in the series resonance circuit. For a morecompleteunderstanding of the invention, reference should be made to theaccompanying drawings wherein:

FIGURE 1 is a schematic diagram of one embodiment of the presentinvention;

FIGURE 2 is a schemiatic diagram of an alternative embodiment of thepresent invention;

FIGURES 3, 4 and 5 show wave forms used in exice plaining the operationof the circuits of FIGURES 1 and 2.

Referring to FIGURE 1 in detail, the numeral 10 indicates generally atransformer having a primary winding 12 and a secondary winding 14. Theprimary winding has a tap at 16. Typically, the primary winding hasforty-four turns with the tap being at sixteen turns from one end,indicated 18, which end is also connected to one end of the secondary14. In a typical automobile ignition system, the common end 18 of theprimary and secondary windings is connected to ground potential and theother end of the secondary is connected to the distributor. Thesecondary winding may have in the order of ten thousand to fifteenthousand turns. The primary and secondary windings are wound on a closedloop core made of saturable magnetic material. While square hysteresisloop material such as ferrite may be used, less square loop materialsuch as grain oriented 4 mil Hypersil material has been found suitable.

The ungrounded end of the primary 12 is connected to the positive sideof a standard 12 volt automobile battery through a series capacitor 20and an inductor 22. In addition, a ballast resistor 24 may be providedin the series circuit having a bypass switch 26 which is closed wheneverthe automobile starter is engaged.

An NPN silicon transistor 30 has its collector connected at the seriesjunction point between the capacitor 20 and inductor 22 and its emitterterminal connected to the tap 16 on the primary of the transformer 10. Abias resistor 32 connects the base electrode of the transistor 30 to theemitter electrode. The transistor 30, which is controlled in the mannerhereinafter described by the ignition breaker points, is normallyconducting. Thus a low impedance current path is provided from thepositive terminal of the battery through the inductor 22, through thesixteen turn portion of the primary winding of the transformer 10 to thegrounded negative terminal of the battery. When the transistor 30 ismomentarily turned off, providing an open circuit, the capacitor 20 ischarged up to a high peak voltage by the collapse of the magnetic fieldof the inductor 22. As the capacitor 20 continues to charge, the voltagereverses across the primary of the transformer 10 and then begins to gopositive again. The transistor switch 30 is then closed again and allthe energy stored in the capacitor 20 is discharged through the primaryof the transformer 10, producing a negative saturation of thetransformer. When the transformer saturates, a flux reversal occurs withthe charge on the capacitor being dissipated very rapidly producing alarge positive peak. This source of current begins charging the inductorcausing a series of small oscillations between the transformer 10 andseries capacitor 20. FIGURE 3 shows the voltage Wave form across thecapacitor 20. The voltage wave form as shown in FIGURE 4 corresponds tothe voltages observed across the primary winding of the transformer,while FIGURE 5 shows the corresponding wave form across the secondarywinding.

Control of the transistor switch 30 in the arrangement of FIGURE 1 isfrom the breaker points indicated generally as a switch 34. The switch34 controls an NPN transistor 36 having its base normally connected tothe positive side of the battery through a pair of resistors 38 andAli). The breaker point 34, when closed, connects the junction betweenthe resistor 38 and the resistor 40 to the grounded terminal of thebattery. The collector of the transistor 36 is connected through a loadresistor 42 to the positive terminal of the battery through the ballastresistor 24. The emitter of the transistor 36 is connected to groundpotential through a bias resistor 4-4. Thus when the breaker points areclosed, the transistor 36 is rendered nonconductive, and when thebreaker points 34 open, the transistor 36 becomes conductive.

The emitter of the transistor 36 is connected through a couplingcapacitor 46 to the base of a PNP transistor 48. The base of thetransistor 48 is also connected to ground potential through a biasresistor 50. The emitter of the transistor 47 is connected to thepositive terminal of the battery while the collector is connectedthrough a resistor 52 to the base of the transistor 30.

In operation, when the breaker points open, the transistor 36 is turnedon. This produces a positive going signal at the emitter of thetransistor 36 which, in turn, provides a positive going pulse across thedifferentiating circuit formed by the capacitor 46 and resistor 50. Thispulse occurring on the base of the transistor 48 momentarily turns offthe transistor 48. When the transistor 48 is on, the transistor 30 isbiased on, but when the transistor 48 is turned off by the positivegoing pulse applied to the base thereof, the transistor switch 30 ismomentarily turned off. Both the transistor 48 and resistor 30 turn backon again after an interval determined by the time constant of thecapacitor 46 and resistor 50.

A capacitor 54 connects the collector electrode of the transistor 36 toground potential. The capacitor 54 in combination with the resistor 42provides a relatively constant voltage source for the transistor 36 sothat the timing pulse for the transistor 48 is more uniform underchanging voltage conditions, such as occur in starting or due to a weakbattery.

The circuit arrangement of FIGURE 2 is a modification of theabove-described circuit of FIGURE 1 and differs only in the pulsingcircuit for the transistor switch 30. The same reference characters areused in FIGURE 2 to identify circuit components which are the same as inFIG- URE 1. The circuit arrangement of FIGURE 2 has the advantage thatit utilizes NPN transistors for all three stages.

In the arrangement of FIGURE 2, the collector of the transistor 36 iscoupled through a capacitor 60 to the base of an NPN transistor 62. Thebase of the transistor 62 is also connected through a biasing resistor64 to the positive terminal of the battery. The collector of thetransistor 62 is connected through a load resistor 66 to the positiveterminal of the battery. Both the emitter of the transistor 36 and theemitter of the transistor 30 are directly connected to the tap 16 on theprimary of the transformer 10. The base of the transistor 62 isconnected to the collector of the transistor 30 through a diode 70 andthe zener diode 72.

In operation, when the circuit breaker points 34 open, the transistor 36is turned on producing a negative pulse at the base of the transistor62. This pulse momentarily turns off the transistor 62 and turns off theswitching transistor 30.

As pointed out above, as the capacitor 20 charges, the tap 16 on theprimary of the transformer goes below ground. Although the voltage onthe base of the transistor 62 tends to rise as the capacitor 60discharges through the resistor 64, the fact that the emitter of thetransistor 36 is dropping below ground results in the transistor 62being held nonconductive for a period of time that ensures that thetransistor 30 is not prematurely turned on before the pulsing circuitcan completely cycle. The zener diode limits the voltage to which thecapacitor 20 charges regardless of changes in the supply voltage. Whenthe potential at the collector rises in relation to the potential at thebase of transistor 62 to the breakdown potential of the zener diode, thetransistor 62 is turned on sooner and the charging action interrupted.The diode 70 blocks reverse current flow from the base of the transistor62 through the zener diode in the forward direction.

The zener diode is important in that it permits effective .operation ofthe circuit over a wide range of supply voltage, e.g., six volts whenstarting to as high as volts when the car generator is charging at ahigh rate. It eliminates the need for the bypass switch startingarrangement described in connection with FIGURE 1 and at the same timeprotects against an over voltage condition.

From the above description, it will be recognized that a high voltageignition circuit is provided in which a comparatively low current flowsthrough the transformer more or less constantly and is interrupted onlymomentarily to charge the storage capacitor 20. This circuit is designedto provide an interruption period of approximately two hundredmicroseconds. When the current begins to flow again with the turning onof the transistor 30, a new charging cycle for the inductance 22commences. This short interruption makes possible the use of a chargingchoke drawing substantially less current than that required for theconventional ignition coil. By having a separate inductance, an optimumcharging choke design can be achieved without the necessity ofcompromise in favor of high voltage considerations, as is required wherethe inductance is part of the high voltage coil.

It is also important that when the transistor 30 again turns on andpulses the transformer, the resulting high voltage pulse is concurrentwith the beginning of the recharging cycle of the inductance 22. Thusthe charging cycle for the inductance does not have to be suspendeduntil the high voltage output oscillations have subsided as in theconventional type of ignition system.

In recent developments of coils for transistorized systems, it has beenfound necessary to use high current drain primary coils as a measure toreduce working voltages and still retain good high speedcharacteristics. This is not necessary with the present inventionbecause of the substantially greater on time available to charge theinductance 22. As a result, a lower charging current is required than inconventional ignition systems.

The fact that the present circuit requires a comparatively small primaryand no cooling for the coil makes possible the design of a very compacttransformer unit which may be connected directly to the center lead of aconventional distributor cap. The result is a more compact design thanit is now possible to achieve with conventional high voltage coils.

What is claimed is:

1. An internal combustion ignition circuit controlled in response to theopening and closing of a switch for generating a high voltage pulse froma standard battery source, said circuit comprising a transformer havinga saturable core and primary and secondarly windings, the secondaryhaving a large number of turns in relation to the primary, the primaryhaving an intermediate tap, one end of the primary and secondarywindings being connected to one side of the battery source, a capacitorand inductor connected in series between the other end of the primaryand the other side of the battery source with the capacitor beingconnected between said other end of the primary winding and theinductor, normally closed switch means connecting the series connectionpoint be tween the inductor and capacitor to said tap, and means formomentarily opening the switch means to start the generation of a highvoltage on the secondary.

2. An ignition circuit for generating a high voltage from a low voltagedirect current source comprising a transformer having a primary windingand a secondary Winding having a large number of turns in relation tothe primary, means including an inductance and capacitance connectingthe primary across said source, the inductance and capacitance being inseries circuit with the primary across the source, and a normally closedswitch connecting the junction between the inductance and capacitance toan intermediate tap on the primary, the switch being opened momentarilyto initiate the generation of high voltage oscillations at the output ofthe secondary.

3. An ignition circuit for generating high voltage oscillations from alow voltage direct current source in response to the opening of aswitch, comprising an output transformer having a primary and a highvoltage secondary, a capacitor and inductor connecting in series betweenone end of the primary and one end of the source, the other end of theprimary being connected to the other end of the source, a firsttransistor having its emitter-collector circuit connected between a tapon the transformer primary and the common connection between theinductor and capacitor, a resistor connecting the base of the firsttransistor to the emitter, a second transistor "having itsemitter-collector circuit connected between the base and one terminal ofthe source so as to form a biasing current through said resistor whenthe second transistor is conducting in a direction to turn on the firsttransistor, and means including a third transistor responsive to theopening of said switch for turning off the second transistor for apredetermined time interval.

4. Apparatus as defined in claim 3 wherein said lastnamed means furtherincludes a resistance-capacitance differentiating circuit coupled to thebase of the second transistor to control said time interval.

5. Apparatus as defined in claim 3 wherein all three transistors are ofthe same conductive type and the emitter of the first and thirdtransistors are connected to the tap on the transformer primary.

6. Apparatus as defined in claim 5 further including a zener diodeconnected between the collector of the first transistor and the base ofthe second transistor.

7. An ignition circuit for generating a high voltage signal from a lowvoltage direct current source comprising first, second and thirdtransistors of the same conductive type, each transistor having a base,an emitter and a collector electrode, an output transformer having atapped primary and high voltage secondary, a storage capacitor connectedin series with one end of the primary, an inductor connected between thecapacitor and one side of the source, the other side of the source beingconnected to the opposite end of the primary, the emitters of the firstand third transistors being connected to the tap on the primary, thecollector of the third transistor being connected to the common junctionbetween the capacitor and inductor, a bias resistor connecting betweenthe base and emitter of the third transistor, a first load resistorconnects between the collector of the first transistor and said one sideof the source, a second load resistor connected between the collector ofthe second transistor and said one side of the source, a capacitorconnected between the collector of the first transistor and the base ofthe second transistor, a bias resistor connected between the base of thesecond transistor and said one side of the source, the emitter of thesecond transistor being connected to the base of the third transistor,and means coupled to the base of the first transistor for turning thefirst transistor off and on.

8. Apparatus as defined in claim 7 further including a zener diodeconnected between the collector of the first transistor and the base ofthe second transistor and a diode in series with the zener diodeconnected to block current flow through the zener diode in the forwarddirection.

References (Jilted by the Examiner UNITED STATES PATENTS 2,898,3928/1959 Jaeschke.

3,078,391 2/1963 Bunodiere et al.

3,131,327 4/1964 Quinn 123-148 X 3,169,212 2/1965 Walters.

MARK NEWMAN, Primary Examiner.

LAURENCE M. GOODRIDGE, Examiner.

1. AN INTERNAL COMBUSTION IGNITION CIRCUIT CONTROLLED IN RESPONSE TO THEOPENING AND CLOSING OF SWITCH FOR GENERATING A HIGH VOLTAGE PULSE FROM ASTANDARD BATTERY SOURCE, SAID CIRCUIT COMPRISING A TRANSFORMER HAVING ASATURABLE CORE AND PRIMARY AND SECONDARDLY WINDINGS, THE SECONDARYHAVING A LARGE NUMBER OF TURNS IN RELATION TO THE PRIMARY, THE PRIMARYHAVING AN INTERMEDIATE TAP, ONE END OF THE PRIMARY AND SECONDARYWINDINGS BEING CONNECTED TO ONE SIDE OF THE BATTERY SOURCE, A CAPACITORAND INDUCTOR CONNECTED IN SERIES BETWEEN THE OTHER END OF THE PRIMARYAND THE OTHER SIDE OF THE BATTERY SOURCE WITH THE CAPACITOR BEINGCONNECTED BETWEEN SAID OTHER END OF THE PRIMARY WINDING AND THEINDUCTOR, NORMALLY CLOSED SWITCH MEANS CONNECTING THE SERIES CONNECTIONPOINT BETWEEN THE INDUCTOR AND CAPACITOR TO SAID TAP, AND MEANS FORMOMENTARILY OPENING THE SWITCH MEANS TO START THE GENERATION OF A HIGHVOLTAGE ON THE SECONDARY.